1. Field of the Invention
The present invention relates to an antenna apparatus, and more particularly to an antenna apparatus used for receiving electric waves of a global positioning system (GPS), a satellite radio, and the like.
2. Description of Related Art
For example, an antenna apparatus illustrated in FIG. 7 was developed as an antenna apparatus to be used for an in-car GPS system, which was spread as a positioning system, and an antenna apparatus to be used for in-car or a in-home fixed type satellite radio, which was put to practical use in US (see, for example, Japanese Patent Application Laid-Open Publications No. Hei 11-74671, No. 2001-68175, and No. 2005-109688).
In the example of the antenna apparatus 100, a circuit substrate 103 is stuck on the back of an antenna element 102 having a patch type receiving surface 101 receiving electric waves. A not shown circuit amplifying an input from the antenna element 102 is formed on the surface on the opposite side of the circuit substrate 103 to the antenna element 102, and the surface on which the circuit is formed is covered by a substantially box-like shield cover 104.
The shield cover 104 is made of a metal to shield the circuit from disturbing waves from the outside. Moreover, the base surface 104a of the substantially box-like shield cover 104 is disposed in parallel with the receiving surface 101 of the antenna element 102. Incidentally, the receiving surface 101 of the antenna element 102 is drawn to be thicker than the actual thickness thereof in FIG. 7.
A coaxial cable 105 is inserted into the shield cover 104. The core wire 105a of the coaxial cable 105 is connected to the circuit on the circuit substrate 103 by being soldered to the circuit. The coaxial cable 105 supplies driving power to the circuit, and outputs a signal that has been received by the antenna element 102 and amplified by the circuit.
Moreover, the shield cover 104 also functions as the ground (GND), and a tongue flap 104b is formed on the shield cover 104 to be bent from the base surface 104a of the shield cover 104 to the side of the coaxial cable 105. The tongue flap 104b is then connected to the outer conductor 105b of the coaxial cable 105 by being soldered to the outer conductor 105b with solder H, and thereby the shield cover 104 is set to the GND potential through the tongue flap 104b. The circuit substrate 103 is grounded through the shield cover 104.
Various structures were conventionally proposed as the structure of the tongue flap 104b of the shield cover 104. For example, Japanese Patent Application Laid-Open Publication No. Hei 11-74671 discloses the tongue flap 104b which is bent substantially perpendicularly to the base surface 104a of the shield cover 104 and the end of which is formed to an arcuate notch along the outer conductor 105b of the coaxial cable 105 on the side of the coaxial cable 105, as shown in FIG. 8.
Incidentally, FIG. 8 shows the circuit substrate 103, the shield cover 104 and the coaxial cable 105 in the case where the antenna apparatus 100 of FIG. 7 is turned upside down, and omits to show the soldering between the tongue flap 104b of the shield cover 104 and the outer conductor 105b of the coaxial cable 105.
Moreover, Japanese Patent Application Laid-Open Publication No. 2003-17154 discloses the tongue flap that is similarly bent from the base surface 104a of the shield cover 104 toward the coaxial cable 105 not substantially perpendicularly from the base surface 104a like the tongue flap 104b shown in FIG. 8, but is bent obliquely, although the tongue flap is not shown. Japanese Patent Application Laid-Open Publication No. 2003-17154 proposes to ground the shield cover by bringing the tongue flap into elastic contact with the outer conductor of the coaxial cable so that the tongue flap may press the outer conductor without soldering the tongue flap to the outer conductor.
However, the aforesaid tongue flap structure in the antenna apparatus described in Japanese Patent Application Laid-Open Publication No. 2003-17154 has the possibility that the strength of the elastic contact of the tongue flap to the outer conductor of the coaxial cable lowers with time to produce a contact failure owing to the influences of the vibrations of a car, and the like, for example, the antenna apparatus is for in-car use. Moreover, because the connection portion between the tubular outer conductor of the coaxial cable and the tabular tongue flap is in the state of point contact, the efficiency of the grounding of the shield cover lowers.
In this respect, in the antenna apparatus described in Japanese Patent Application Laid-Open Publication No. Hei 11-74671, because the connection portion between the tongue flap 104b and the outer conductor 105b of the coaxial cable 105 is soldered, no bad connection is caused. Moreover, because the connection area between the tongue flap 104b and the outer conductor 105b in the connection portion can be enlarged, the grounding efficiency of the shield cover 104 through the tongue flap 104b can be sufficiently secured.
However, as to the tongue flaps 104b shown in FIGS. 7 and 8, the solder H in the connection portions sometimes rises higher than the heights of the base surfaces 104a of the shield covers 104 at the time of the soldering of the tongue flaps 104b to the outer conductors 105b of the coaxial cables 105. If the antenna apparatus 100 in which the solder H rises like this is, for example, placed on a horizontal surface with a bottom cover 106 put between them, as shown in FIG. 9, then the receiving surface 101 of the antenna element 102 inclines to the horizontal surface shown by an alternate long and short dash line in FIG. 9. Consequently, the directivity of the antenna becomes worse, and the reception efficiency of electric waves lowers. Moreover, the assembly accuracy of the antenna apparatus 100 also lowers.
Moreover, in the aforesaid antenna apparatus for the GPS system, the satellite radio, and the like, which antenna apparatus receives a high frequency signal and amplifies the received signal, the improvement of the grounding efficiency of the circuit substrate is regarded as a vital problem. The improvement of the grounding efficiency is frequently achieved by making the bottom cover 106 of a metal, and by bringing the bottom cover 106 and the base surface 104a of the shield cover 104 into surface contact.
If the solder H rises higher than the height of the base surface 104a of the shield cover 104 at the connection portion of the tongue flap 104b with the outer conductor 105b of the coaxial cable 105 in the antenna apparatus like this, then the base surface 104a of the shield cover 104 rises from the bottom cover 106 as shown in FIG. 9, and the bottom cover 106 and the shield cover 104 cannot be brought into the surface contact. Consequently, it becomes impossible to improve the grounding efficiency.
If the solder rises in a connection portion, various problems are caused as described above. Accordingly, it is needed to prevent the solder from rising at the time of manufacturing antenna apparatus. However, if the soldering of connection portions is carefully performed one by one, the manufacturing efficiency of the antenna apparatus lowers. Consequently, the soldering structure is required that can perform soldering without raising the solder in a connection portion or without raising the solder not to be higher than the height of the base surface 104a of the shield cover 104 even if the solder rises by performing an ordinary soldering operation.